Cook sushi rice using a rice cooker according to manufacturer's instructions, combining 4 cups of rice with the appropriate amount of water. Let sit for 10 minutes to cool before mixing in salt and furikake.

Dice the chicken into small pieces and combine with soy sauce, sake, baking soda, and cornstarch in a bowl. Cover and refrigerate for at least 30 minutes.

Whisk together soy sauce, mirin, and brown sugar to create the teriyaki sauce. Set aside.

Heat oil in a pan, add marinated chicken, and sauté for 2-3 minutes until fully cooked. Add garlic, cooking for an additional 30 seconds, then remove from heat.

Return chicken to the pan and pour in the teriyaki sauce, stirring to coat and cooking until sauce thickens, about 2-3 minutes.

Wet hands and scoop ⅓ cup of rice, forming a well. Place chicken filling in the well, add another ⅓ cup of rice on top, shape into a triangle, and wrap with nori.

Serve the shaped onigiri warm or at room temperature with pickled vegetables or edamame.